Units of that type are known, in which the shelves are fixed to the uprights in various manners. Units exist in which the shelves are not adjustable, in which case battens or the like or used as fixing systems for fixing the shelves. Units also exist in which the uprights are in a plurality of portions, each of which is equipped with end-pieces that co-operate with bores provided at all four corners of the shelves.
Units also exist in which the shelves are adjustable, and in which the shelves rest on rests which can be displaced vertically along racks provided on the uprights.